In 2003, the United States Department of Energy completed a full‐scale non–aqueous phase liquid (NAPL) remediation of Area A of the Northeast Site at the Young‐Rainey STAR Center, Largo, Florida. Area A covered an area of 930 m2 (10,000 square feet) and extended to a depth of 10.7 m (35 feet), representing a total cleanup volume of 9930 m3 (12,960 cubic yards). The site was contaminated with ∼2500 kg (5500 lb) of NAPL constituents such as trichloroethylene, cis‐1,2‐dichloroethylene, methylene chloride, toluene, and petroleum hydrocarbons. The site consists of a fine‐grained sand aquifer underlain by a Hawthorn clay at 9 m (30 feet) depth. The upper 1.5 m (5 feet) of this clay formed part of the remediation volume, as dense non–aqueous phase liquid was present in this layer. The site was remediated using a combination of steam‐enhanced extraction and electrical resistance heating. Operations lasted 4.5 months. The site was heated to the target temperatures within 6 weeks, at which time the mass removal rate increased more than 1000‐fold. After the target volume had been heated to or near boiling temperatures, pressure cycles were used to increase the mass removal rates, until a final phase of diminishing returns was reached. Postoperational sampling of soil and ground water at randomly selected locations showed the concentrations of all contaminants of concern (COC) to be well below the remedial goals. The majority of the ground water samples were below maximum contaminant level (MCL) for all the COC. The estimate of volatile organic contaminant (VOC) mass removed from the site (1130 kg = 2500 lb) agreed well with the estimate of VOC present before operation (1170 kg = 2580 lb). The postoperational sampling showed that ∼0.5 kg (1 pound) of VOCs remained in the remedial volume, and showed remedial efficiencies of between 99.85% and 99.99% for the four chemicals of concern. Since the postoperational sampling shows all concentrations to be below or close to ground water MCLs, the thermal remedy may be satisfactory for site closure without a polishing phase.

Dense nonaqueous phase liquid (DNAPL) source areas containing chlorinated volatile organic compounds (cVOCs) such as trichloroethene (TCE) and perchloroethene (PCE) often give rise to significant dissolved plumes in groundwater, leading to the closure of downgradient water supply wells and creating vapor intrusion issues in buildings located above the plume. Hydraulic containment via pump‐and‐treat has often been implemented to limit migration but must continue indefinitely. Removal of the DNAPL source area by means such as in situ thermal remediation (ISTR) offers the potential to diminish or end the need for hydraulic containment if the associated dissolved plume attenuates sufficiently following source removal. A question often raised is whether this occurs or whether the back diffusion of contaminants from secondary sources such as low‐permeability lenses in the dissolved plume precludes it. The authors conducted DNAPL source removal using ISTR at dozens of sites. This paper presents a compilation of cases—10 separate DNAPL source areas at five project sites—where data indicate that the implementation of a thorough ISTR in a DNAPL source area can result in the attenuation of the associated dissolved plume, such that in several cases, long‐standing pump‐and‐treat systems could be turned off. Our findings contrast with recent assertions that aggressive source remediation may not be justifiable because dissolved plume concentrations will not decline sufficiently. We show that the application of ISTR can result in the thorough removal of the DNAPL source, effective diminution of dissolved plume groundwater concentrations, and achievement of drinking water standards.

In situ thermal remediation technologies provide efficient and reliable cleanup of contaminated soil and groundwater, but at a high cost of environmental impacts and resource depletion due to the large amounts of energy and materials consumed. This study provides a detailed investigation of four in situ thermal remediation technologies (steam enhanced extraction, thermal conduction heating, electrical resistance heating, and radio frequency heating) in order to (1) compare the life‐cycle environmental impacts and resource consumption associated with each thermal technology, and (2) identify options to reduce these adverse effects. The study identifies a number of options for environmental optimization of in situ thermal remediation. In general, environmental optimization can be achieved by increasing the percentage of heating supplied in off peak electricity demand periods as this reduces the pressure on coal‐based electricity and thereby reduces the environmental impacts due to electricity production by up to 10%. Furthermore, reducing the amount of concrete in the vapor cap by using a concrete sandwich construction can potentially reduce the environmental impacts due to the vapor cap by up to 75%. Moreover, a number of technology‐specific improvements were identified, for instance by the substitution of stainless steel types in wells, heaters, and liners used in thermal conduction heating, thus reducing the nickel consumption by 45%. The combined effect of introducing all the suggested improvements is a 10 to 21% decrease in environmental impacts and an 8 to 20% decrease in resource depletion depending on the thermal remediation technology considered. The energy consumption was found to be the main contributor to most types of environmental impacts; this will, however, depend on the electricity production mix in the studied region. The combined improvement potential is therefore to a large extent controlled by the reduction/improvement of energy consumption.